Event-related brain potentials (ERPs), and concomitant behavioral indices will be recorded from normal subjects during studies of cognitive development and aging and from two clinical populations, schizophrenics and patients with Alzheimer's disease, who display specific cognitive deficits. It is expected that the ERP measures will provide insights into the hierarchy, sequencing and timing of information processing that are much more difficult to infer from behavioral data alone. The main goal in the study of normal subjects is a description and analysis of the changes in the electrical activity of the normally aging brain, with a view toward a better understanding of age-related changes in semantic processing and memory function. In the study of schizophrenia and Alzheimer's disease, the cognitive ERPs will be elicited during tasks designed specifically to tap the functions for which these disordered subjects show deficits. Comparison of the disordered groups' ERPs with those recorded from normal samples will allow an assessment of which stages of information processing are deficient in these populations and should, in turn, allow more precise functional definitions of the endogenous ERP components. During the tenure of the award, the principal investigator will develop greater expertise in the application of topographical methods to the cognitive ERPs and, via collaboration and consultation, will gain additional knowledge in the area of risk research, in the application of cognitive methodology to development and aging, and in the application of ERP technology to patients with localized brain damage.